The present invention relates to a radio transmission apparatus, and more particular to a radio transmission apparatus for constructing a route of a radio network by employing a directional antenna.
Conventionally, the radio transmission apparatus of this type was employed in the event of configuring the radio network by employing the directional antenna in an inter-base-station network in a mobile communication system (cellular system), and in an ad hoc network for autonomously configuring a network without connection to a wire network.
The routing in the network is composed of the process of grasping a state of the network by exchanging a routing packet by node companions capable of making communication. By the routing packet, the control is taken so that a total route cost for reaching a specific communication destination is recognized, and such a route that the cost becomes minimum is employed.
In the wire network, only node companions connected by means of a cable are capable of making communication; however, in the radio network, there is a status that it is impossible to grasp which node is a node capable of making communication. For this reason, it is necessary to predetermine the route for constructing the network, or to make a scheme in which the network is autonomously constructed in consideration of characteristics of the radio. Inter-base-station communication in the cellular system is made by means of the former technique in many cases, and the ad hoc network corresponds to the latter.
The inter-base-station network in the cellular system is not only configured to employ the wire such as an optical fiber, but also is configured to employ a fixed radio apparatus and the directional antenna in some cases. In a system having such a configuration, the route is designed in advance in installing a base station because of communication between fixed stations, and directivity of the antenna is regulated to the route for the node of a connection destination to fix it. In this case, there is no necessity for causing both of the routing and the directional regulation to act harmoniously for control in the directional regulation of the antenna because a radio station of the connection destination was pre-decided at the time of designing.
On the other hand, the ad hoc network does not require the node such as the base station and a control station, which makes management in a concentrated manner, and terminal companions employ the radio to autonomously configure the network. In such a network, in making communication between specific nodes, the other node, which is positioned between the nodes that make communication, relays the packet in the event that direct communication is impossible due to the problem of the transmission distance.
This example is shown in FIG. 9. The terminal companions tied up by lines in the figure are presumed to be able to communicate with each other by means of a radio link. In the same figure, it is impossible for a terminal A to directly communicate with a terminal D; however communication is possible by relaying the packet via the other node. For example, when the packet is relayed via a terminal B, the packet reaches the terminal D by two-hop transmission. Or, when the packet is relayed via both of a terminal C and a terminal E, its transmission becomes three-hop transmission. In such a manner, communication is possible to make by utilizing the relay by the other node in the ad hoc network; however, the route to a communication partner needs to be established prior to communication whenever it is made, because it is assumed that the position of the terminals varies.
An omnidirectional antenna is employed in many cases in the ad hoc network system, and the routing packet for establishing the route, and a data packet for transmitting data are sent almost in all directions by employing the identical antenna. It is a purposive service method to transmit the packet in all directions by employing the omnidirectional antenna in the packet transmission for establishing the route; however when the omnidirectional antenna is employed for communication of data, radio waves result in being radiated in a direction other than the direction of the terminal to which the packed is desirably sent, whereby interference is apt to occur, which is not effective.
An example of the ad hoc network employing the directional antenna was described in JP-P2001-244983A. In the routing method described in this JP-P2001-244983A, in generating the route, a SINR (signal power to interference noise power ratio) of a signal (pre-determined training pattern) to be sent from surrounding terminals was measured together with received direction information, and its information was employed for the directional control at the time of transmission. After the direction information of the surrounding terminals and information of the SINR were collected, a search for the route up to the communication partner is made.
At this moment, each node have already held a routing table, and recorded the relaying number (hop number) required in the event of communicating with the node of the communication partner, and the node that became a closest route destination. An operation is as follows in the event of searching for the route to the node of the communication partner that does not exist in the above routing table, or to the node of the communication partner of which the entry available period expired already even though it exists.
At first, the terminal recorded in the routing table, which can be reached at one hop from its own node, is asked as to whether direct communication is possible to make with the communication partner desired for communication. Said direction information is employed to regulate the directivity in transmitting the signal for asking the terminal. In the event that communication is impossible to make with any first-hop terminal, next, the routing table is confirmed to ask the terminals that can be reached at two hops. By repeating such an operation in order of the node, beginning with the node that can be reached at one hop, and in order of the SINR, beginning with a large value, the route to the communication partner desired for communication is discovered. This method allows the route, of which the hop number up to the communication destination becomes minimum, and of which the SINR up to the first-hop relay terminal becomes maximum, to be selected.
However, the conventional network system as mentioned above has the problems as described below.
Route generation in the network is made, by employing the routing packet to select the route of which the route cost up to the communication partner becomes minimum. The relaying number (hop number) ranging the node, which initiates communication, up to its destination is often employed for the route cost, however the sum etc. of the inverse number of the SINR of each inter-node radio link is employed in the radio network. So as to carry out such a routing that the route cost is minimized, it is necessary for a certain node to propagate the routing packet in the surrounding nodes. Additionally, on the other hand, at the moment that the route is decided, and data is transmitted by employing this route, it is effective from the viewpoint of interference restrain and a gain to employ the directional antenna to transmit data. Accordingly, in the event of employing the directional antenna to transmit data, a necessity occurs for transmitting a signal in all directions to generate an appropriate route, and for regulating a direction of the directional antenna to the generated route.
It is possible to design the network in advance for deciding the route, as is the case with the conventional base-station network construction; however the node is added and the route is changed in some cases due to increase in the user number, generation of obstacles between the routes, and so forth after initiation of the service. In this case, the network has to be re-designed once again and the directivity of the antenna has to be regulated for the node of which the connection destination is changed, which takes much time and labor.
Also, cooperation between the routing and the directional control is carried out in the ad hoc network employing the directional antenna; however only a measurement value between its own node and the surrounding node is employed in the conventional example (JP-P2001-244983A), whereby, in consideration of efficiency of the entire system, it can not always be said to become a best-suited value. For example, in the network like FIG. 9, now assume that two three-hop routes of terminal A→B→D→F (route 1) and terminal A→C→E→F (route 2) exist for communication from a terminal A to a terminal F. In the event that this two routes were treated as a candidate, as to the SINR between the terminal A and its neighboring node, the SINR between the terminals A and C, which exists at a closer position, is normally larger than that between the terminals A and B; however as to the total SINR of the entire route, the route 1 is larger in some cases because the distance between the terminals E and F is longer, and pass loss becomes larger. At this time, the route 2 is selected in the method of the conventional example because only the SINR up to the neighboring node is confirmed. However the route 1 is selected in the event that the routing packet was employed to select the route. In such a manner, taking a consideration into the entire route ranging the node, which initiates communication, up to the destination node, if only quality for its own node and the neighboring node is taken as a selection criterion, the inadequate route results in being selected in some cases.
Also, in the routing method of the ad hoc network, it is premised that the location of each node is frequently changed, and furthermore, each node decides the route for each destination by itself, whereby its method is unsuitable for the inter-base-station network etc. of the cellular system in which the nodes are arranged in a fixed manner.
Thus, the present invention has been accomplished so as to solve the above-mentioned tasks, and an objective thereof is to provide a radio transmission apparatus, a routing method, and a routing program of the radio network that, in employing the directional antenna to construct the radio network, make it possible to autonomously control the directivity of the antenna in parallel with route generation employing the routing packet.
Furthermore, another objective of the present invention is to provide a radio transmission apparatus, a routing method, and a routing program of the radio network that make it possible to simultaneously carry out the routing of both nodes that are positioned upstream and downstream respectively, and the directional control of the antenna in the radio network.